Many attempts have been made to utilize filters in a flowing stream and at the same time clean (all or) part of the filters in order that the flowing stream will not be stopped. One prior art system, found in U.S. Pat. No. 2,173,060, teaches an apparatus that backflushes filter elements by regurgitating the entrained particles of the element but does not meet current needs.
Another attempt to provide clean filter elements in a fluid stream is taught in U.S. Pat. No. 3,833,121, wherein two filters are positioned in one housing so that one clean filter is always onstream. When the onstream filter becomes dirty, there are means for transferring the uninterrupted fluid flow to the clean filter. After the flow has been transferred from the dirty filter, the dirty filter is removed from the offstream side of the unit, cleaned and replaced. Although this device works quite satisfactorily, it does not obviate the necessity for removing a filter from the unit and cleaning it separately in an external operation.
Thus, none of the prior art provides a satisfactory method or device to clean part of a filter while onstream and yet remove the dirty contaminates generated during the backflushing cycle completely from the system.